This invention relates generally to contamination-free fluid heating systems, and, more specifically to a non-contaminating fluid heater and a safety system for limiting the maximum fluid temperature within the heater and for preventing heater operation under defined circumstances.
With the advent of microchip technology, there has developed a need for systems which utilize contaminant-free fluids. For example, during the manufacturing of computer microchips, acids may be used for etching the microchips and water may be used for rinsing. Because of the small scale of today's microcircuits and the high manufacturing tolerances required, virtually any impurity in the etching or rinsing fluid can result in defective parts and wasted resources.
To provide the necessary high-purity fluid for use in such systems, filtering processes are employed to remove virtually all contaminants and, effectively, de-ionize the fluid. The systems are further designed to prevent contact between the contaminant-free fluid and any substance which would tend to corrode in the presence of the fluid, causing impurities to be reintroduced.
Many systems require the contaminant-free fluid to be heated above ambient temperatures to meet required design and manufacturing parameters. Heater manufacturers have sought to design acceptable devices which are thermally efficient, responsive to fluid flow changes, and capable of long life. Although most plastic materials tend to be good thermal insulators and therefore seemingly inappropriate for some uses in heating systems, most modern heaters for use in microchip manufacturing systems must employ plastics to shield the contaminant-free fluid from the metallic heating element, lead wires and the like.
Because thermally insulative material must be used to shield the metallic portion of the heating element from the contaminant-free fluid, much more power is utilized by the heater than would be required in the absence of the insulative shielding. Therefore, the heating coil must usually remain completely submerged within the heated fluid or it will overheat and burn. Further, the electrical connection between the lead wires and the heating element is usually submerged into the heated fluid and subjected to its sometimes corrosive nature.
Attempts have been made to provide a seal about the electrical connection between the lead wires from the power source and the heating element, to protect that connection from the heated fluid and to prevent any leaching of contaminants from the wires into the fluid. The failure to adequately protect this electrical connection has been a problem area for heater manufacturers and users. More specifically, imperfections in sealing techniques often result in failure of the system (exposure of the metallic portion of the heating element or lead wire), requiring repurification of the fluid and replacement of the heater. The useful life of many prior heaters and heating systems is determined primarily by the lifetime of the environmental sealing means surrounding this electrical connection.
An acceptable seal for the electrical connection between the lead wires from the power source to the heating element, which overcomes the limitations and drawbacks of the prior art, is shown and described in my co-pending U.S. patent application Ser. No. 06/913,505, filed Sept. 29, 1986, now U.S. Pat. No. 4,756,781.
Heaters and heating systems for use in microchip manufacturing processes are inherently expensive due to the precise nature of their construction and the materials required for such. It is thus very important that extraordinary measures be taken to ensure proper operation of the non-contaminating heating system, including measures to prevent overheating of the fluid and the heating coils.
Accordingly, there has been a need for a novel non-contaminating fluid heater capable of use with a broad spectrum of fluids, in a variety of operational configurations and within a broad range of temperatures. In this regard, there has been a need for a heating system and associated heater hardware which lends itself readily to a variety of power/flow configurations to accommodate varying needs of prospective users. Additionally, there exists a need for non-contaminating fluid heating systems which can efficiently and economically heat and maintain the fluid passing therethrough at a desired temperature. Further, a fluid heater is needed which is durable and capable of long, sustained use in harsh environments. Moreover, a fluid heater and control system is needed for preventing damage to the heater components and for ensuring that the fluid will be heated only to temperatures within acceptable limits. The present invention fulfills these needs and provides other related advantages.